Duplex Baseband Signal Transmission Over Free Space Optical (FSO) Link Employing Carrier Reuse

Abstract

With increasing IoT and a plethora of multimedia applications being used, there is an ever-increasing demand for bandwidth-intensive applications coupled with cost-effectiveness. Communication networks employing optical fiber had been de facto standard for such communication systems. The Optical Fiber network's high cost and man-hours required for laying demand wireless solutions. Therefore, an optimum and cost-effective duplex optical link for two channels baseband signal data transmission has been designed and validated using a single laser source. The link is designed for high data rate transmission between buildings within 1.5~2 km utilizing modular and low complexity. An optical link for 20 Gb/s duplex data transmission is designed using a single laser source. A transmission distance of 1.5 km has been achieved by providing a cost-efficient design with low complexity by utilizing differential quadrature phase shift keying (DQPSK) and On-Off Keying (OOK) modulation techniques. The design allowed us to reuse the downlink signal for the uplink transmission over free Space, thus eliminating the requirement for a separate laser at the other end. Each channel's transmission data rate was 10Gb/sec. At the former end, the DQPSK technique was employed for data modulation and the data was transmitted into free space. The data was then split at the latter end for downlink reception along with reusing the downlink received signal for uplink transmission to the former end utilizing the OOK modulation technique. The received data was compared with the transmitted one to verify and validate the system's accuracy through signal waveforms and BER (Bit Error Rate). Bit error rate (BER) curves and eye diagrams of the received uplink and downlink signal over a duplex transmission single fiber link are provided.